When performing laser eye surgery such as when ablating a target region on a patient's cornea with a refractive laser beam system, it is beneficial to have accurate information on the dimensions of the laser beam spot which is incident on the cornea. Deviation from a desired spot size and shape, such as by increased or decreased diameter of the laser beam spot or by the spot exhibiting an oval or non-symmetrical shape, could result in tissue ablation at undesired locations on the patient's corneas with each laser pulse, leading to less than ideal resculpting. Inaccuracy in the location of the laser spots may result in off-center ablations.